The invention relates to a mounting structure of a grounding terminal on a printed circuit board, wherein the printed circuit board is grounded to a grounding conductor by the grounding terminal, which is mounted on the surface of the printed circuit board by reflow soldering, contacting with and being pressed against the grounding conductor.
Conventionally, a mounting structure of a grounding terminal on a printed circuit board for grounding the printed circuit board, in which a grounding terminal is mounted on the surface of the printed circuit board and pressed against a grounding conductor, is known. FIG. 5 is a plan view of such a conventional grounding structure and FIG. 6 is a longitudinal sectional view along line VIxe2x80x94VI of FIG. 5. As shown in FIG. 6, the grounding terminal 100 is soldered to the conductive pattern 201 on the printed circuit board 200 with solder 202. Then, the grounding terminal 100 is pressed against the grounding conductor, thereby grounding the printed circuit board 200. To illustrate the structure simply, the grounding conductor 300 is not shown in FIG. 5.
The grounding terminal 100 is formed by bending a strip-like thin sheet metal member with a width of xcex1, for example, 0.8 mm, and has a joint part 101 with a longitudinal length of xcex2, for example, 3.5 mm. One surface of the joint part 101 is a joint surface 101a which is soldered to the conductive pattern 201 on the printed circuit board 200. Also, the grounding terminal has a contact part 102 which adjoins the joint part 101 and is bent in the upper direction. An outer surface 102a of the contact part 102 is pressed against the grounding conductor 300. As the result of load by the grounding conductor, the contact part 102 is elastically deformed around the bending area xcex3, and is pressed against the grounding conductor 300 by restoring force caused by the elastic deformation, thereby electrically connecting the printed circuit board 200 and the grounding conductor 300 properly.
When the aforementioned grounding terminal is soldered to the printed circuit board, reflow soldering is usually employed. Reflow soldering comprises the steps of previously applying a suitable amount of solder to the point to be jointed, fixing the grounding terminal to the point temporarily, and melting the solder by using an external heat source, and all these steps are performed automatically. An advantage of reflow soldering is that by allowing a suitable amount of solder to be applied, it prevents solder from being placed at inappropriate points of the printed circuit board, and thus prevents improper soldering such as a defective bridge. Also, there is another advantage that in the case where a relatively small mounting member as aforementioned is to be mounted, self-alignment effect can be expected. That is, even if the temporarily fixed member deviates a little from the conductive pattern of the printed circuit board, the member is moved to the right position by surface tension of the melted solder.
However, there are the following problems in reflow soldering of the above conventional grounding terminal:
(1) The grounding terminal 100 is moved to the right position by self-alignment effect by surface tension of the melted solder, and then is finally positioned by hardening of the melted solder. During the hardening process of the solder, the grounding terminal 100 sometimes deviates from the right position on the printed circuit board 200 because of, for example, vibration. This results from the fact that since the amount of the solder is large, the thermal capacity of the solder is large, and thus it takes time for the solder to harden. If the grounding terminal 100 deviates from the right position, the contact part 102 may not be pressed against the grounding conductor 300 in an appropriate state. Furthermore, the requirements of highly precise mounting performance for allowing high density mounting are not satisfied.
(2) When the temperature of the grounding terminal 100 reaches the melting point of the solder earlier than that of the conductive pattern 201 of the printed circuit board 200, what is called wicking phenomenon occurs, by which the solder 202 is sucked up along the bending area xcex3 forming the center of elastic deformation of the contact part 102 shown in FIG. 6. In this case, since the solder 202 adheres around the bending area xcex3, the elastic deformation performance of the contact part 102 is lowered, and thus it is sometimes impossible to attain elastic deformation enough for the contact part 102 to be pressed against the grounding conductor 300 and conduct electricity to the grounding conductor 300.
Wherefore, an object of the invention is to provide a mounting structure of a ground terminal on a printed circuit board formed by soldering, wherein by solving the problems caused by reflow soldering of the grounding terminal to the printed circuit board, the printed circuit board is properly grounded to a grounding conductor.
Another object of the invention is to provide a grounding terminal used for the above mounting structure.
In order to achieve the above objects, there is provided a grounding terminal mounted on a printed circuit board which is able to have contact with a grounding conductor, the grounding terminal comprising: a joint part having a plurality of joint surfaces which are to be soldered to a conductive pattern on the printed circuit board; a contact part extending from the joint part through a bending area bent in the opposite direction of the joint surfaces, and arranged to be able to have contact with the grounding conductor, which is elastically deformed upon being pressed by the grounding conductor; and at least one of the contact surfaces of the joint part having a smaller surface area than those of the other contact surfaces.
Also, there is provided a mounting structure in which a grounding terminal able to have contact with a grounding conductor is mounted on a printed circuit board, the grounding terminal comprising: a joint part having a plurality of joint surfaces which are to be soldered to a conductive pattern on the printed circuit board; a contact part extending from the joint part through a bending area bent in the opposite direction of the joint surfaces, and arranged to be able to have contact with the grounding conductor, which is elastically deformed upon being pressed by the grounding conductor; at least one of the contact surfaces of the joint part having a smaller surface area than those of the other contact surfaces; and the grounding terminal being mounted on the printed circuit board by reflow soldering, using an amount of solder corresponding to the surface area of each joint surface.